The handling and processing of tomatoes requires inter alia that an enormous quantity of tomatoes be individually inspected and that culls, normally spoiled and/or green tomatoes, be removed. To perform this task manually is laborious and expensive; moreover there is an inherent subjective variation in the acceptance-rejection criteria to be followed.
To overcome this problem, automatic tomato sorters have recently become available. Normally, such sorters are constructed so that they can be used in conjunction with automatic tomato harvesting equipment such as is disclosed, for example, in U.S. Pat. Nos. 3,193,020 and 3,390,768. The tomato harvester described in these patents is driven through tomato fields, removes the tomatoes from the vines and deposits them on one or more tomato collection belts. The belts transport the tomatoes to a loading conveyor which discharges the tomatoes into trucks or the like drawn alongside the harvester.
The automatic tomato sorters are positioned so that they intercept the flow of tomatoes on the collection belts, normally by arranging the tomatoes on a belt in a multiplicity of parallel rows and by individually viewing each tomato. If a tomato is determined to be a cull, e.g. if it is unacceptably green, a reject mechanism is energized which removes the tomato from the tomato flow and, normally discharges such cull onto the ground. The remaining tomatoes continue their normal course towards the discharge point.
In the past, the tomatoes were optically inspected by sensing an image of each tomato via suitable filters with a photo-sensitive device such as a photo-multiplier. The output of the photo-multipliers is supplied to a corresponding pair of matched logarithmic amplifiers the output of which is in turn sent to a summing amplifier for generating a red/green ratio signal. If the ratio signal exceeds a predetermined threshold, a reject signal is generated which energizes the reject mechanism and ejects the cull from the tomato flow.
Although such color sorters were a great improvement over the earlier manual sorting methods, the optics employed by them was sensitive and susceptible to error readings. The formation of a ratio signal requires first of all that the photo-multipliers receive light from the same point (on the tomato) and at the same time. Otherwise, the ratio signal is meaningless and the respective output signals are error signals which may lead to the rejection of a good tomato or to the acceptance of a cull.
When the image of the tomato is sensed by the photo-multipliers, great care must be taken that one of the photo-multipliers does not receive a predominant portion of its light from one part of the tomato while the other photo-multiplier receives a predominant portion of its light from another part of the tomato. Even the slightest misalignment of the components of the optics can lead to such a result. Accordingly, prior art systems of the type discussed above had to be manufactured with the utmost precision which, in turn, rendered them relatively expensive. Moreover, they required correspondingly more maintenance.
Lastly, in the rough environment of a tomato harvester, with continuous shock, vibration, dust and the like, slight optical misalignments could at times occur during use of the sorter. Any of these events can result in prolonged and expensive machine downtimes to effect the necessary repair. Since the tomato harvesting season is normally very short, a machine downtime of only a few days could seriously shorten the usefulness of the harvester for that year. In addition, if slight misalignments go undetected during harvesting operations large quantities of tomatoes, normally in the order of hundreds of tons for only a single day's production, might be rejected by processing plants due to an unacceptably high level of culls, e.g. green tomatoes in the total mass of tomatoes. In such an event, the tomatoes must be re-sorted, frequently an impossible task, or they must be discarded. In either event, the economic loss to the farmer is very large.